The present invention relates to a urethane-modified polyisocyanurate foam having a high expansion rate, which is excellent in flame retardancy and heat resistance, and is low in smoke generation, without using chlorofluorocarbons (CFCs) or hydrochlorofluorocarbons (HCFCs) as a blowing agent.
In the polyurethane and polyisocyanurate industries, because of a problem of depleting the ozone layer, use of CFCs, which had been used as versatile and effective blowing agents, has been banned since 1995, and further, even HCFCs, substitutes for CFCs, having much lower ozone depletion potential, are scheduled to be banned from the year of 2003. Hence, a variety of alternative blowing agents, such as hydrofluorocarbons (HFC), hydrocarbons (HC), carbon dioxide (CO2), etc. are being studied.
It is said lately that HCFC blowing is being replaced by the CO2 blowing for the polyurethane foam (PUR system) for insulated metal sidings or panels, and that the replacement has been almost completed.
However, in the case of the polyisocyanurate foam (PIR system), which is rated high for the flame retardancy and heat resistance, when the CO2 blowing method is applied, there are specific problems of lower than typical flame retardancy, heat resistance and shrinkage (deformation) with time, in addition to a problem of unsatisfactory adhesion to a facing material, not allowing the replacement of the conventional blowing method by the CO2 blowing to develop as successfully as in the case of PUR systems.
In the CO2 blowing method, it is generally said that a foam causes shrinkage (deformation) with time. This is because of the rapid diffusion of CO2 from the foam cells.
In the field of insulated metal sidings or panels cored with the PUR system, the replacement by the CO2 blowing method has been almost completed by lowering a closed cell ratio as a means for preventing shrinkage (deformation) with time. For example, by employing a combination of a high molecular polyol and a low molecular polyol, the resulting foam becomes rich with open cells and, because of its low density, does not cause shrinkage.
In the field of insulated metal sidings or panels cored with the PIR system, a foam having an open cell structure can be obtained to prevent shrinkage (deformation) by employing a method of using certain aromatic polyester polyols (JP-A-10-231345), and a method of producing a foam of relatively low density by using a trimerization catalyst and a carbodiimide-forming catalyst in combination (Japanese Patent No. 2,972,523), but there are problems of lowering flame retardancy, heat resistance and a poor adhesion to a facing material, and it is therefore difficult to use the CO2 blowing as a substitute for the conventional blowing methods.
In order to solve the above-mentioned problems of a PIR type foam employing a CO2 blowing agent, it is necessary not only to make a foam having a continuous cell phase (open cells) for improving the shrinkage problem but also to solve the above-mentioned problems concerning flame retardancy and heat resistance.
In order to solve the above-mentioned problems, the present inventors have discovered a novel method not only for freely controlling a cell size but also for improving flame retardancy and heat resistance by applying a benzylic ether type phenolic resin (hereinafter referred to as xe2x80x9cBEPxe2x80x9d) to the PIR system.
Particularly, flame retardancy and heat resistance are improved by employing BEP as a polyol component and a cell size is controlled by mixing surfactants, having different properties, at an appropriate ratio. For example, a silicone type surfactant is used as a foam stabilizer (1) and a dimethylsilicone oil is used as a foam stabilizer (2).
More particularly, the present invention provides a urethane-modified polyisocyanurate foam obtained by reacting (A) a polyisocyanate compound component, (B) a polyol component (said polyol component contains a modified phenolic resin (hereinafter referred to as xe2x80x9cmodified BEPxe2x80x9d) obtained by adding 20 to 100 parts by weight of a polyhydric alcohol or its alkylene oxide adduct to 100 parts by weight of a benzylic ether type phenolic resin and heating under a reduced pressure, in an amount of at least 3 wt % to the total resin component), (C) water and (D) a foam stabilizer comprising a mixture of at least 2 silicone type surfactants having different surface tensions wherein a surfactant having a higher surface tension has a surface tension of higher than 22 dyne/cm and a surfactant having a lower surface tension has a surface tension of at most 22 dyne/cm, in the presence of (E) a urethane-forming catalyst and/or a trimerization catalyst.
The polyol component (B) used in the present invention is a mixture of modified BEP and a polyol generally used for producing a urethane foam. Thus, the polyol component (B) comprises mainly modified BEP by adding 20 to 100 parts by weight of a polyhydric alcohol or its alkylene oxide adduct to 100 parts by weight of a benzylic ether type phenolic resin and heating the mixture under a reduced pressure, as described in JP-B-7-30155. Examples of other polyols usable with the modified BEP include difunctional polyols such as ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, polytetramethylene glycol, 1,4-butanediol or these difunctional polyols addition-polymerized with one or two or more kinds of alkylene oxides, trifunctional polyols such as trimethylolpropane, glycerin or these trifunctional polyols addition-polymerized with alkylene oxides, polyfunctional polyols such as pentaerythritol, sorbitol, sugar or these polyfunctional polyols addition-polymerized with an alkylene oxide, an aromatic polyester polyol, an acryl polyol resin, and the like, and these polyols may be used alone or may be used in a mixture of two or more polyols. The modified BEP is used suitably in an amount of at least 3.0 wt to the total resin component. If the amount of the modified BEP is less than 3.0 wt %, flame retardancy, heat resistance and low smoking property become poor.
A polyisocyanate compound (A) used in the present invention is not specially limited and may be ones generally used in the preparation of a polyurethane foam, examples of which include m- or p-phenylene diisocyanate, p-xylene diisocyanate, ethylene diisocyanate, tetramethylene 1,4-diisocyanate, hexamethylene-1,6-diisocyanate, diphenylmethane-4,4xe2x80x2-diisocyanate, 3,3xe2x80x2-dimethyldiphenylmethane-4,4xe2x80x2-diisocyanate, 3,3-dichloro-4,4xe2x80x2-biphenylene diisocyanate or 1,5-naphthalene diisocyanate, 2,4- and 2,6-tolylene diisocyanate and their mixture, crude tolylene diisocyanate, 4,4xe2x80x2-diphenylmethane diisocyanate, crude diphenylmethane diisocyanate, and the like. These isocyanate compounds may be used alone or in a mixture of two or more. Its amount used is an equivalent ratio of an isocyanate group/active hydrogen in a polyol component mixture solution in a range of from 1.05 to 5.0, preferably from 1.50 to 3.0. If the above equivalent ratio is less than 1.05, flame retardancy, heat resistance and low smoking property become poor, and if the equivalent ratio is more than 5.0, a foam produced becomes brittle and adhesiveness to a facing material becomes poor.
A foam stabilizer used in the present invention is a mixture of at least two kinds of silicone type surfactants having different surface tensions, and a component having a higher surface tension has a surface tension higher than 22 dyne/cm. A foam stabilizer generally used in the preparation of a urethane foam may be used, preferable example of which include an organic polysiloxane copolymer, a polydimethylsiloxanexc2x7polyalkylene oxide adduct, a vinylsilanexc2x7polyoxyalkylene polyol compound and the like. A component having a lower surface tension has a surface tension lower than 22 dyne/cm, preferable examples of which include a dimethylsilicone oil.
Examples of the organic polysiloxane copolymer include SH-190, SH-192, SH-193, SH-194, M505, M507, M509 and SRX253 manufactured by Toray Silicone K.K., L-520, L-540, L-580, L-582, L-5340, L-5410, L-5420, L-5470 and SZ-1127 manufactured by UNICAR CO., LTD., TFA-4200, TFA-4205 and TFA-7241 manufactured by Toshiba Silicone K.K., and B-8404 and B-8017 manufactured by GOLDSCHMIDT K.K.
Examples of the dimethylsilicone oil include SH-200 manufactured by Toray Silicone K.K., and TSF-451-5, TSF451-50 and TSF405 manufactured by Toshiba Silicone K.K.
A suitable mixing ratio of a component having a higher surface tension/a component having a lower surface tension is 100 parts by weight/0.5-50 parts by weight. If the amount of the component having a lower surface tension is less than 0.5 part by weight, the aimed effect of the present invention can not be achieved, and shrinkage is caused. On the other hand, if the amount of the component having a lower surface tension is more than 50 parts by weight, a foam-breaking effect becomes large and a satisfactory foam can not be obtained. A foam stabilizer (D) comprising a mixture of at least two kinds of silicone type surfactants having different surface tensions is used preferably in an amount of from 0.5 to 10 parts by weight to 100 parts by weight of a polyol component (B).
A catalyst used for carrying out urethane-foaming reaction may be ones generally known as a urethane-foaming catalyst, examples of which include N,N,Nxe2x80x2,Nxe2x80x2-tetramethylethylenediamine, N,N,Nxe2x80x2,Nxe2x80x2-tetramethylpropane-1,3-diamine, N,N,Nxe2x80x2,Nxe2x80x2-tetramethylhexene-1,6-diamine, N,N,Nxe2x80x2,Nxe2x80x3,Nxe2x80x3-pentamethyldiethylenetriamine, N,N-dicylcohexylmethylamine, bis(N,N-dimethylaminoethylpiperazyl)ethane, N,Nxe2x80x2,Nxe2x80x3-tris(diethylaminopropyl)hexahydrotriazine and other tertiary amine, and dibutyltin dilaurate, dibutyltin diacetate, and the like. These catalysts may be used alone or in a mixture thereof.
An isocyanate trimerization catalyst used in the present invention may be a trimerization catalyst for isocyanates used in the preparation of a conventional polyisocyanurate resin. Examples of the isocyanate trimerization catalyst include an organic metal salt system such as potassium acetate, potassium octenate, iron oxalate or the like, a tertiary amine salt such as 2,4,6-tris(dimethylaminomethyl)phenol, N,Nxe2x80x2,Nxe2x80x3-tris(dimethylaminopropyl)hexahydrotriazine or the like.
An urethane-foaming catalyst and a trimerization catalyst (E) are used in an amount of from 0.3 to 15 parts by weight, preferably from 0.70 to 10 parts by weight to 100 parts by weight of a polyol component (B).
Water (C) used in the present invention reacts with a polyisocyanate compound to produce carbon dioxide and works as a foaming agent. An amount of water is determined depending on an aimed density of a foam, and is suitably from 2 to 30 parts by weight to 100 parts by weight of a polyol component (B). If the amount of water is less than 2 parts by weight, a density of a foam becomes too high, and if the amount of water exceeds 30 parts by weight, a mechanical strength becomes too low for practical use.
In the present invention, if necessary, a crosslinking agent and a viscosity-reducing agent may be used. Examples of the crosslinking agent include ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, triethylene glycol, triethanolamine, ethylenediamine or the like, and they may be used alone or in a combination of two or more. Examples of the viscosity-reducing agent include nitrogen-containing type, sulfur-containing type, phosphorus type, ether type, hydrocarbon type, ester type or carbonate type organic compounds which are liquid at normal temperature, and they may be used alone or in a combination of two or more. These additives and other additives may be previously mixed with a mixture containing a polyol component (B) or may be added thereto at the time of reacting.
In the production of a polyisocyanurate foam of the present invention, a high pressure foaming machine, a medium pressure foaming machine or a low pressure foaming machine is used to produce a board, a panel or a siding in a factory or to carry out in-situ foaming.